The petroleum industry is increasingly turning to coal, tar sands, heavy crudes and distilled residual oils as sources for feedstocks. Feedstocks derived from these heavy materials often contain more sulfur and nitrogen than feedstocks derived from more conventional crude oils and are commonly referred to as being dirty feeds. These feeds require a considerable amount of upgrading before being introduced into processes which make lighter products such as fuel oil or gasoline. Such upgrading or refining generally is accomplished by the hydrotreating processes which are well-known in the petroleum industry.
Hydrotreating processes may require the step of treating the hydrocarbon with hydrogen or a catalytic material to convert at least a portion of the feedstocks to lower molecular weight hydrocarbons, or to remove unwanted components, or compounds, or to convert them into innocuous or less undesirable compounds. Hydrotreating may be applied to a variety of feedstocks, e.g., solvents, light, middle, or heavy distillate feeds and residual feeds, or fuels. In hydrorefining relatively light feeds, the feeds are treated with hydrogen, often to improve odor, color, stability, combustion characteristics, and the like. Unsaturated hydrocarbons are often hydrogenated to saturation. Sulfur and nitrogen are occasionally removed as part of such treatments. In the treatment of catalytic cracking feedstocks, the cracking quality of the feedstock is generally improved by the hydrotreating in that elemental carbon yield is reduced and gasoline yield is increased. In the hydrodesulfurization ("HDS") of heavier feedstocks, or residua, the sulfur compounds are hydrogenated and cracked. Carbon-sulfur bonds are broken, and the sulfur, for the most part, is converted to hydrogen sulfide which is removed as a gas from the process. Hydrodenitrogenation ("HDN"), to some degree, also accompanies hydrodesulfurization reactions. In the hydrodesulfurization of relatively heavy feedstocks, emphasis is on the removal of sulfur from the feedstock.
Catalysts most commonly used for hydrotreating reactions include materials such as cobalt molybdate on alumina, nickel on alumina, colbalt molybdate promoted with nickel, nickel tungstate, etc. Molybdenum sulfide is also used to upgrade oils containing sulfur and nitrogen compounds by catalytically removing such compounds in the presence of hydrogen, which processes are collectively known as hydrotreating or hydrorefining processes, it being understood that hydrorefining also includes some hydrogenation of aromatic and unsaturated aliphatic hydrocarbons. Thus, U.S. Pat. No. 2,914,462 discloses the use of molybdenum sulfide for hydrodesulfurizing gas oil and U.S. Pat. No. 3,148,135 discloses the use of molybdenum sulfide for hydrorefining sulfur and nitrogen-containing hydrocarbon oils. U.S. Pat. No. 2,715,603 discloses the use of molybdenum sulfide as a catalyst for the hydrogenation of heavy oils, while U.S. Pat. No. 3,074,783 discloses the use of molybdenum sulfides for producing sulfur-free hydrogen and carbon dioxide, wherein the molybdenum sulfide converts carbonyl sulfide to hydrogen sulfide. Molybdenum sulfide has other uses in catalysis, including hydrogenation, methanation, water gas shift, etc., reactions.
Catalysts comprising molybdenum sulfide in combination with other metal sulfides are also known. Thus, U.S. Pat. No. 2,891,003 discloses an iron-chromium combination for desulfurizing olefinic gasoline fractions; 3,116,234 discloses Cr-Mo and also Mo with Fe and/or Cr and/or Ni for HDS; 3,265,615 discloses Cr-Mo for HDN and HDS; 3,245,903 discloses Fe-Mo and Fe-Co-Mo for lube oil refining; 3,459,656 discloses Ni-Co-Mo for HDS; 4,108,761 discloses Fe-Ni-Mo for HDN and 4,171,258 discloses Fe-Cr-Mo for HDS with steam.
Additionally, Gleim et al, U.S. Pat. No. 3,165,463 and Gatsis '958, U.S. Pat. No. 3,269,958, suggest the use of a non-supported Group VIB, VB or iron group metal as a hydroprocessing catalyst. The catalyst is made by admixing a hydrocarbon feedstock with an organo-metallic compound and decomposing the compound to form a colloidal suspension which is then sulfided. Examples 11 and 111 therein appear to show mixed Mo and Ni catalysts. Gatsis '556, U.S. Pat. No. 3,249,556, suggests a similar process. The Group VIB, VB or iron group metal, in organometallic form, is mixed with a hydrocarbon feedstock, and the resulting colloidal suspension is reacted with hydrogen. The resulting reaction mixture is separated to provide a catalyst containing sludge which, in turn, is hydrogenated in the presence of an iodine-containing compound to form a catalyst suitable for recycle to the feedstock hydrocarbon.
Gatsis '874, U.S. Pat. No. 3,262,874, suggests a variation of the above-noted processes in which the catalyst is the decomposition product of a mixture of a heteropoly acid and nickelous sulfate.
Gleim '302, U.S. Pat. No. 3,271,302, and Gatis '769, U.S. Pat. No. 3,331,769, suggest a variation in which one or more of the noted materials is placed on an inorganic support.
The use of nickel to promote various sulfide catalysts has been reported. See, Burmistov et al, Catalytic Properties of Ni/WS.sub.2 Samples in Thiophene Hydrogenalysis, React. Kinet. Catal. Lett., 24, pp. 365-369 (1984) and Zaikovskii, TEM and XPS Studies of Ni/WS.sub.2 Catalysts for Thiophene Hydrogenalysis, React. Kinet. Catal. Leit., 24, pp. 17-22.
None of the above-cited prior art discloses a molybdenum or tungsten sulfide catalyst suitable for hydroprocessing in which the molybdenum or tungsten sulfide is promoted by use of low-valent transition metal compounds.